WO2008/043701 discloses pharmaceutical solid dosage forms comprising a therapeutically effective compound (i.e. a drug) micro-embedded into an ionic water-insoluble polymer matrix. A preferred micro-embedding process involves depositing an ethanolic solution of a therapeutically effective compound and an ionic water-insoluble polymer on microcrystalline cellulose (MCC) spheres using a fluid bed coater. The disclosed water-insoluble polymers include those which are only soluble in water above pH 5.5. EUDRAGIT L100-55, a methacrylic acid copolymer, is listed as a suitable water-insoluble polymer that meets this definition. The MCC spheres, coated with the drug/ionic water-insoluble polymer, were further coated with a distinct, protective seal coat consisting of polyvinylpyrrolidone (PVP) and calcium silicate. PVP and calcium silicate were added in two separate steps to ethyl alcohol (200 proof) to form the seal coating suspension. A seal coat is used to protect the drug from direct exposure to ambient storage conditions. While the function of the calcium silicate is not discussed in WO2008/043701, it is noteworthy that the calcium silicate is part of a separate coating layer from the methacrylic acid copolymer with no plasticizer included. There is therefore no beneficial interaction between the methacrylic acid copolymer and calcium silicate.
U.S. Pat. No. 6,420,473 describes dry enteric film coating compositions comprising an acrylic resin, an alkalizing agent, a detackifier and, optionally, additional ingredients such as plasticizers, flow aids, pigments, surfactants, anti-agglomerating agents, secondary film formers and secondary detackifiers. Calcium silicate is not listed in the '473 patent, and the concept of a reversible plasticizer sequestrant was not disclosed therein.
While the formulations disclosed in U.S. Pat. No. 6,420,473 are commercially useful, there is still a need for improved pH dependent coatings that can be applied at lower coating weight gains than prior art coatings to shorten overall process times.